Early-life exposures are known to be crucial for shaping the developing immune system but the processes involved are poorly understood. Petter Brodin and colleagues have performed longitudinal immune profiling of blood from newborn infants and report that the individual immune phenotypes seen at birth are highly diverse; however, infant immune systems then seem to converge on a shared developmental pathway in the first few weeks after birth, despite differences in environmental exposures. They propose a model of ‘stereotypic immune system development’, in which the exposure of infants to many diverse environmental stimuli after birth (some of which will have opposing effects) leads to the convergence of initially diverse immune systems.
Epidemiological studies have suggested that an individual’s susceptibility to developing immune-mediated diseases later in life can be crucially shaped in the first 100 days after birth. However, it has been difficult to characterize the immune system during this critical period of life owing to difficulties in obtaining blood samples from healthy children. Olin et al. undertook a systems-level analysis of the blood and plasma components of 100 newborn humans, assessing up to 4 blood samples from the same child in the first 3 months of life. For these longitudinal studies, the authors developed a protocol that allowed them to obtain meaningful data using as little as 100 μl of blood. The cohort consisted of 50 very premature children (born at less than 30 weeks of gestation) and 50 full-term infants (born after 37 weeks). Of note, the initial early-life exposure of these groups differed drastically, as preterm children had longer hospital stays, frequent treatment with antibiotics and an increased rate of infections compared with term children.
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